1. Field of the Invention
The present invention relates to a tape measure, and more particularly to a tape measure in which its tape can be extended outward by itself and which is also extended and retracted by turning its handle.
2. Description of the Prior Art
A conventional tape measure has a case, a scale tape, a spool and a leaf spring for retracting the scale tape. Upon using the tape measure, the user pulls the scale tape from the case to measure a length of an object. After the measurement, the scale tape is retracted into the case and wound on the spool by restoring force of the leaf spring.
In order to use the above type of tape measure, the user must pull a desired length of the scale tape by his hand. Also, the tape measure must have the leaf spring having a length proportional to that of the scale tape (for example, a five meter tape measure requires about 3.5 meter length of a leaf spring). When the tape measure has an eight meter length of a scale tape, it requires a stronger leaf spring.
Accordingly, it is difficult to manufacture the longer leaf spring in technique and the longer leaf spring causes a high manufacturing cost of the tape measure. Furthermore, the above tape measure can not be used for a long time because of inferiority, breakage and rust of the leaf spring.